The present invention relates to a method of fastening a driving band and/or a pipe cap to the body of a projectile or other ammunition unit, such as an artillery shell.
Projectiles with large calibres are generally provided with a driving band fastened to the rear part of the projectile to obturate the bore of the barrel and to cause the projectile to rotate in the barrel as it is fired therefrom due to the barrel rifling. The driving band is generally made of a softer material than the rest of the shell, mainly to reduce the wear of the barrel rifling.
In order to prevent the propellant gases to reach the payload of the projectile or other ammunition unit it is previously known to provide the rear surface of the projectile with a shielding cover such as for instance a plate or cap, a so called pipe cap, designed to resist the gas pressure and high temperatures produced in the barrel on firing.
When manufacturing projectiles the driving band and the pipe cap are usually fastened separately on the projectile body. For fastening the driving band on the body of an artillery shell it is common to use press fits or a combination of press and shrinkage fits. Due to new requirements for increased velocities and ranges, however, there is a risk that such conventional press or shrinkage fits are not sufficiently strong to retain the driving band in its place on account of the forces which influence the driving band on firing from the barrel.
New methods of fastening a driving band to the envelope surface of a projectile have therefore been developed. One such new method is fasteneing the driving band to the envelope surface of the projectile by means of friction welding.
Pipe caps are usually made of metal, for instance steel, and are used for protecting the surface of the projectile on which the propellant gases are actuating and they have previously been fastened by means of conventional welding or soldering.
Both these methods are relatively expensive, however. Even if the friction welding of a driving band in many applications gives a satisfactory strength, there is a risk that the driving band will come loose when it is exposed to extremely high speeds during firing. Furthermore the fastening of the pipe cap presents difficulties especially for projectiles in which the rear surface, for aerodynamical reasons, is cap shaped.